[citation needed] A proposed variant with more powerful engines designated the Caproni Ca.325 was built only in mock-up form.

General Valle (Chief of Staff of the Regia Aeronautica) initiated the "R-plan" – a program designed to modernize Italy's air force, and to give it a strength of 3,000 aircraft by 1940.

However, the project was retained at Ponte San Pietro and the prototype, completed during 1934–35 (a long construction time for the period), was first flown on 1 April.

The prototype was powered by two 623 kW (835 hp) (at 4,000 m/13,000 ft) Isotta Fraschini Asso XI.RC radial engines initially fitted with two bladed wooden propellers.

Its long nose accommodated the bomb-aimer (bombardier) and a front turret (similar to the Piaggio P.108 and later British bombers).

The wireless operator's station, in the aft fuselage, was fitted with the AR350/AR5 (the standard for Italian bombers), a radiogoniometer (P63N), an OMI AGR.90 photographic-planimetric machine or the similar AGR 61.

There was almost no chance of carrying a full load of fuel with the maximum bombload, (other Italian bombers were generally capable of a 3,300–3,600 kg/7,300–7,900 lb payload).

The production version was fitted with two inline liquid-cooled Asso XI RC.40 engines, each giving 671 kW (900 hp) at 4,000 m (13,000 ft).

These Tipo Spagna ("Spanish Type") aircraft were refitted with Fiat A.80 R.C.41 engines, rated at 746 kW (1,000 hp).

With the scrapping of the first batch and the selling of the second, all 64 Ca.135s left the service of the Regia Aeronautica without performing a single operational mission.

The Magyar Királyi Honvéd Légierő (MKHL; the Royal Hungarian Air Force) ordered Ca.135s which were delivered in 1940 and 1942 in two series of 36 rsp.

The Hungarians operated a total of 67 Ca.135bis with some success against the Soviet Union on the Eastern Front in 1941 and 1942, once Hungary had committed its forces in that sector during World War II.

[1] When Hungary declared war on the Soviet Union in June 1941, the Hungarian Air Force was almost entirely equipped with Italian aircraft.

That day, 1st Lt Istvan Szakonyi, in his Ca.135 from the 4/III Bomber Group, managed to destroy an important bridge with a 'trial drop' of two bombs.

[2] The Ca.135s equipped the 3./III Group of 3rd Bomber Wing, based in Debrecen, a bomber unit of the Hungarian air formation commanded by Lt Col Béla Orosz, that had been tasked to provide air support to the Hungarian Rapid Corps, subordinated to the German 17th Army.

[3] On 11 August, six Capronis, commanded by 1st Lt Szakonyi, took off to bomb a 2 km (6,560 ft) bridge across the Bug River of the city of Nikolayev, on the Black Sea.

One Ca.135 had to turn back due to engine problems, but the other five, escorted by Hungarian Fiat CR.42s and MÁVAG Héja Is, continued eastwards.

Szakonyi's Caproni was hit by AA fire and lost his port engine but the squadron commander remained in action.

After the German 11th Army captured Nikolayev, on 16 August, the commander of Luftflotte 4, Col Gen Lohr, decorated the successful Hungarian crews at Sutyska.

[4] The Ca.135 on the Eastern Front had frequent malfunctions and its insufficient combat load-carrying capability set high demands on the mechanics maintaining it.

Peru had been considering the replacement of its unsatisfactory Caproni Ca.111 bombers since 1935, and the Italian Air Ministry approved of the foreign sale of the Ca.135.

Caproni test pilot Ettore Wengi made a demonstration flight for the Peruvians which left Silva unimpressed; he viewed the Ca.135 as underpowered and lacking in defensive armament and wrote a letter to the Caproni company insisting on modifications to the aircraft and threatening to cancel the Peruvian order if they were not made.

[6] The resulting version of the aircraft, the Ca.135 Tipo Peru ("Peruvian Type"), had more powerful engines—Isotta Fraschini Asso XI R.C.40 Spinto ("Driven") engines, uprated versions of the Isotta Fraschini R.C.40 Asso ("Ace") delivering 559 kilowatts (750 horsepower) at sea level and 671 kilowatts (900 horsepower) at 4,000 meters (13,123 ft) – and modified engine cowlings with additional openings to accommodate the additional air intakes of the new engines.

The new engines gave the Ca.135 better performance that met the Peruvian requirements, and also allowed an increase in the aircraft's bomb load to 2,000 kilograms (4,409 pounds).

[6] After their pilots had undergone two months of intensive training by Italian officers, five 2nd Heavy Bomber Squadron Ca.135s flew to their permanent base, the Lieutenant Commander Ruiz base, at Chiclayo, Peru, on 5 November 1937, while the sixth bomber remained at Las Palmas to train additional personnel.

[6] In service, the Ca.135 Tipo Peru soon came under criticism, with Peruvian pilots complaining that the bombers yawed to the right on take-off and had poor lateral stability; in addition, their engines proved unreliable in service, and the bombers suffered an excessive number of oil and hydraulic leaks.

They soon were removed from service, disassembled, and carted away on flatbed trucks driven by American military personnel from El Pato airbase.

Although they are rumored to have been burned in the desert or buried somewhere around the El Pato air base, their final fate is unrecorded.

It incorporated a dihedral tailplane and 1,044 kW (1,400 hp) Alfa Romeo 135 RC.32 Tornado radial engines, and given the designation Ca.135 bis/Alfa.